Current collector

ABSTRACT

A current collector for a battery in an implantable medical device is presented. The current collector comprises a material that includes a first surface and a second surface. A first set of apertures extend from the first surface to the second surface of the material. A second set of apertures extend from the first surface to the second surface of the material. The second set of apertures are off-set from the first set of apertures.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of non-provisional U.S. patent application Ser. No. 09/067,208 filed 28 Apr. 1998 and issued 17 May 2005 as U.S. Pat. No. 6,893,772 and entitled, “Current Collector for Lithium Electrode,” which incorporated by reference provisional application 60/072,223 filed Jan. 7, 1998 entitled “SPIRALLY WOUND HIGH RATE ELECTROCHEMICAL CELL”. Additionally, this application is a continuation-in-part of non-provisional U.S. patent application Ser. No. 08/430,532 to Howard et al. for “High Reliability Electrochemical Cell and Electrode Assembly Therefore” filed Apr. 27, 1995 now U.S. Pat. No. 6,051,038, which is a divisional application of U.S. patent application Ser. No. 08/155,410 to Howard et al. for “High Reliability Electrochemical Cell and Electrode Assembly Therefore” filed Nov. 19, 1993 now U.S. Pat. No. 5,439,760, and the entire contents of each are hereby incorporated herein by reference.

FIELD OF THE INVENTION

The present invention generally relates to a battery for an implantable medical device and, more particularly, to a current collector in a battery.

BACKGROUND OF THE INVENTION

Implantable medical devices (IMDs) detect and deliver therapy for a variety of medical conditions in patients. IMDs include implantable pulse generators (IPGs) or implantable cardioverter-defibrillators (ICDs) that deliver electrical stimuli to tissue of a patient. ICDs typically comprise, inter alia, a control module, a capacitor, and a battery that are housed in a hermetically sealed container. When therapy is required by a patient, the control module signals the battery to charge the capacitor, which in turn discharges electrical stimuli to tissue of a patient.

The battery includes a case, a liner, and an electrode assembly. The liner surrounds the electrode assembly to prevent the electrode assembly from contacting the inside of the case. The electrode assembly includes electrodes, an anode and a cathode, with a separator therebetween. Electrolyte, introduced to the electrode assembly, is a medium that facilitates ionic transport and forms a conductive pathway between the anode and cathode. An electrochemical reaction between the electrodes and the electrolyte causes charge to be stored on each electrode.

Typically, the electrode is folded. A fold may include an abrupt or a sharp bend which may affect the separator. It is therefore desirable to develop a current collector that overcomes this potential limitation.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a cutaway perspective view of an implantable medical device (IMD);

FIG. 2 is a cutaway perspective view of a battery in the IMD of FIG. 1;

FIG. 3 is an enlarged view of a portion of the battery depicted in FIG. 2 and designated by line 4;

FIG. 4 is a top angled perspective view of an electrode assembly of the battery depicted in FIG. 2;

FIG. 5 is a side view of an electrode assembly of the battery depicted in FIG. 2;

FIG. 6A is an angled cross-sectional view of a current collector of the battery depicted in FIG. 2;

FIG. 6B is an angled cross-sectional view of the current collector depicted in FIG. 6A and electrode material;

FIG. 7 is a top perspective view of an exemplary current collector that includes substantially triangular-shaped and circular-shaped apertures;

FIGS. 8A-8C are enlarged top views of a portion of the current collector depicted in FIG. 7;

FIG. 9 graphically depicts distance between apertures along the current collector of FIG. 7;

FIG. 10 is a top perspective view of an exemplary current collector that includes circular-shaped apertures;

FIG. 11 is a graph that depicts distance between apertures along the current collector of FIG. 9;

FIG. 12 is graph that depicts relative stiffness of a circular aperture pattern in a current collector;

FIG. 13 is a top perspective view of an exemplary current collector that includes elliptical-shaped apertures;

FIG. 14 is a top perspective view of an exemplary current collector that includes triangular-shaped apertures;

FIG. 15 is a top perspective view of an exemplary current collector that includes oval-shaped apertures;

FIG. 16 is a top perspective view of an exemplary current collector that includes diamond-shaped apertures;

FIG. 17 is a top perspective view of an exemplary current collector that includes rectangular-shaped apertures;

FIG. 18 is graph that depicts relative stiffness of a rectangular aperture pattern in a current collector; and

FIG. 19 is a flow diagram for forming a current collector for a battery.

DETAILED DESCRIPTION

The following description of embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers are used in the drawings to identify similar elements.

The present invention is directed to a current collector for a battery in an implantable medical device. The current collector comprises a material that includes a first surface and a second surface. A first set of apertures extend from the first surface to the second surface of the material. A second set of apertures extends from the first surface to the second surface of the material. The second set of apertures are off-set from the first set of apertures.

The current collector of the present invention uniformly distributes forces on a separator by minimizing local buckling or kinking in the current collector. Reduced local buckling or kinking prevents or minimizes sharp or abrupt bends in the current collector. Reduced local buckling is achieved by ensuring a small variation exists in stiffness across transverse segments of the current collector. Increased uniformity of grid stiffness is also realized with off-sets between centers of the first and the second set of apertures. In one embodiment, the off-set is in the range of about 20 to about 80 degrees(°). In another embodiment, the off-set ranges between 15 and 75°. The current collector of the present invention also “locks” or secures electrode material in place by allowing the electrode material to bond between the apertures. By forming at least one or more bonds between electrode material through the apertures, it is less likely that the electrode material may delaminate from the current collector. The current collector of the present invention may be used in high reliability primary or secondary battery cells (e.g. lithium, lithium alloy) or the like.

FIG. 1 depicts an implantable medical device (IMD) 400. IMD 400 includes a case 402, a control module 404, a battery 406 (e.g. organic electrolyte battery) and capacitor(s) 408. Control module 404 controls one or more sensing and/or stimulation processes from IMD 400 via leads (not shown). Battery 406 includes an insulator 410 disposed therearound. Battery 406 charges capacitor(s) 408 and powers control module 404.

FIGS. 2 through 5 depict details of an exemplary organic electrolyte battery 406. Battery 406 includes an electrode assembly 414 and liquid electrolyte 416, a case 412, and a fill port 481. Electrode assembly 414 includes an anode 415, separator 417, a cathode 419, a liquid electrolyte 416, and a feed-through terminal 418. Anode 415 and cathode 419 each include a current collector 500 (also referred to as a grid), a portion of which is exposed in FIG. 5. Cathode 419 is wound in a plurality of turns, with anode 415 interposed between the turns of the cathode winding. Separator 417 insulates anode 415 from cathode 419 windings. Case 412 also contains the liquid electrolyte 416 to create a conductive path between anode 415 and cathode 419. Electrolyte 416 serves as a medium for migration of ions between anode 415 and cathode 419 during an electrochemical reaction with these electrodes.

Anode 415 is formed of a material selected from Group IA, IIA or IIIB of the periodic table of elements (e.g. lithium, sodium, potassium, etc.), alloys thereof or intermetallic compounds (e.g. Li—Si, Li—B, Li—Si—B etc.). Anode 415 comprises an alkali metal (e.g. lithium, etc.) in metallic form. Cathode 419 may comprise metal oxides (e.g. vanadium oxide, silver vanadium oxide (SVO), manganese dioxide etc.), carbon monofluoride and hybrids thereof (e.g., CF_(X)+MnO₂), combination silver vanadium oxide (CSVO) or other suitable compounds.

FIG. 6A depicts a cross-sectional view of a flexible current collector 500. Current collector 500 is included in either anode 415 or cathode 419. Current collector 500 is a conductive material 502 that includes a first surface 504 and a second surface 506 with a connector tab 520 protruding therefrom. Conductive material 502, which is corrosion-resistant, may be formed of a variety of materials including titanium, titanium alloy, aluminum, aluminum alloy, tantalum, stainless steel, nickel and the like. A first, second, third, and N set of apertures 508, 510, 512, 513, respectively, extend from first surface 504 through second surface 506. N set of apertures are any whole number of apertures. Referring to FIG. 6B, apertures 508, 510, 512, 513 in current collector 500 allows electrode materials to electrostatically interact to form a bond 560 between first and second layers of electrode material 562A, 562B, respectively (e.g. material used to produce an anode or a cathode). Bonding 560 of electrode material 562A, 562B ensures that electrode material 562A, 562B does not delaminate from current collector 500. In this embodiment, first, second, third, and N set of apertures 508, 510, 512, 513 are circular.

FIG. 7 includes substantially triangular-shaped apertures 515 and circular-shaped apertures 517 for first, second, third, and N set of apertures 508, 510, 512, 513. Substantially triangular-shaped aperture 515 is within 20% of the physical dimensions of a perfect triangle whereas circular-shaped aperture 517 is within 5% of the physical dimensions of a perfect circle. As depicted, triangular-shaped aperture 515 includes rounded or curved ends 519A-C and is spaced away from edge 521 (e.g. about 0.0085 inches) and from circular aperture 517 (e.g. about 0.0272 inches), as shown in FIG. 8A. Substantially circular-shaped aperture 517, shown in greater detail in FIG. 8C, includes a diameter of about 0.0315 inches; however, the diameter may be adjusted by a skilled artisan. Substantially circular-shaped aperture 517 almost appears square in shape but includes rounded or curved ends.

Referring to FIG. 8A, second set of apertures 510 is off-set 514 from first set of apertures 508. Off-set 514 is defined as angle a formed between a first and a second aperture 518A, 518B by lines 516A, 516B, and 522. Lines 516A and 516B extend, vertically along vertical plane 530 and perpendicular to horizontal plane 528, from the centers of first and second apertures 518A, 518B, while line 522 connects the centers of first and second apertures 518A, 518B. Angle α generally ranges from about 15° to about 80°. In another embodiment depicted in FIG. 8B, off-set 524 is defined as the amount of horizontal distance along horizontal plane 528 that exists between the centers of third and fourth apertures 538, 540, respectively. Vertical lines 542, 544 intersect centers of apertures 530, 544 respectively and define the outer limits of off-set 524.

Third set of apertures 512 are also off-set 514 from second set of apertures 510. In one embodiment, third set of apertures 512 are substantially aligned with first set of apertures 508. Substantially aligned is defined as first and second set of apertures 508 and 510 within 10 percent of precise alignment measured from the centers of apertures 508 and 510. In another embodiment, third set of apertures 512 may be off-set from both first and second set of apertures 508, 510. Off-set 514 may be about 15° to 75° from second and third set of apertures 510, 512.

First, second, third, and N set of apertures may include a variety of shapes, as shown in FIGS. 10, and 13-17. FIG. 10 includes circular-shaped apertures for first, second, third, and N set of apertures 508, 510, 512, 513, respectively, in current collector 600. In yet another embodiment, FIG. 13 includes substantially elliptical-shaped apertures in first, second, third, and N set of apertures 508, 510, 512, 513, respectively, in current collector 700. In still yet another embodiment, FIG. 14 includes triangular-shaped apertures in first, second, third, and N set of apertures 508, 510, 512, 513, respectively, in current collector 800. In another embodiment, FIG. 15 includes oval-shaped apertures used in first, second, third, and N set of apertures 508, 510, 512, 513, respectively, of current collector 1000. In yet another embodiment, FIG. 16 includes substantially triangular-shaped apertures in first, second, third, and N set of apertures 508, 510, 512, 513, respectively, in current collector 1100. In another embodiment, FIG. 17 includes substantially rectangular-shaped apertures in first, second, third, and N set of apertures 508, 510, 512, 513, respectively, in current collector 1200.

FIG. 9 graphically depicts various distances between apertures along sectional lines A-A, B-B, C-C, and D-D, which minimizes variation and increases uniformity of grid stiffness. As shown, sectional line A-A includes a first spacing between apertures (e.g. about 0.00128 inches); sectional line B-B includes a second spacing between apertures (e.g. about 0.00148 inches); sectional line C-C includes a third spacing between apertures (e.g. about 0.00128 inches); and sectional line D-D includes a fourth spacing between apertures (e.g. about 0.00148 inches).

Beam bending equations under constant moment loading establish the substantially uniform stiffness of current collectors of the present invention. When a uniform beam, which includes a constant section modulus, is loaded under a constant moment, the resultant radius of curvature (R) is equal to the section modulus (EI) divided by the applied moment (M_(t)), and the maximum stress (S) is equal to the moment (M_(t)) times half the beam thickness (t/2) divided by the moment of inertia (I). R=(EI)/M _(t) S=(M _(t) t/2)/I where E is the elastic modulus of the material; I is the moment of inertia; M_(t) is the applied moment; and t is the thickness of the beam.

Assuming that M_(t) is constant and that the beam is fabricated from a single composition, I determines the bending behavior of the beam through the cross-sectional dimensions of the beam. For a rectangular sectioned beam under bending loading conditions, I is defined as: I=(wt ³)/12 where t is the thickness of the beam and w is the width of the beam. If either T or W vary, I changes accordingly. Change in inertia effects a change in both the equilibrium radius of curvature (R) and the maximum stress (S).

Controlling either the local thickness and/or width of current collector 500, achieves a constant I. While control of the thickness is possible, it is believed to be easier to control the width by controlling both the geometry and orientation of the open grid pattern. Assuming a constant grid thickness, the local I can be approximated by summing the total “solid” widths of the perforated beam (Σw) and using the summed value for the width (W) in the equation defining I. I=(wt ³)/12=((Σw)t ³)/12

Since both thickness and the denominator in equations 3 and 4 are constants, the relative I along a beam shaped perforated grid is simply proportional to the summed width of the cross-section at any point along the grid.

Relative stiffness is defined as the ratio of the stiffness at a horizontal position to the maximum stiffness of current collector 500. FIGS. 12 and 18 depict the relative stiffness across the length of current collector 500 in FIG. 5 and current collector of FIG. 9. Maximum uniform stiffness occurs without apertures. FIGS. 9 and 12 show that the relative stiffness decreases at an aperture and increases when tested in areas that lack an aperture. FIG. 18 reveals less uniformity of relative stiffness, as shown by the significantly higher and lower peaks for relative stiffness.

FIG. 19 is a flow diagram for forming an exemplary current collector. At block 1300, a layer of conductive material is provided. At block 1310, a first set of apertures are formed in the layer of material. At block 1320, a second set of apertures are formed in the layer of material. The first and second set of apertures may include a variety of shapes. Exemplary aperture shapes include substantially triangular, circular, rectangular, elliptical, oval, or diamond.

Various alterations can be made which fall within the scope of the present invention. For example, the apertures may be irregular shaped. Additionally, a single current collector may include a variety of different shaped apertures. Furthermore, the present invention encompasses aperture shapes that include at least one triangle or substantially triangular shape. The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention. 

1. A current collector for a battery in an implantable medical device comprising: a material which includes a first surface and a second surface; a first set of apertures that extend from the first surface to the second surface of the material; and a second set of apertures that extend from the first surface to the second surface of the material, the second set of apertures off-set from the first set of apertures.
 2. The current collector of claim 1, wherein the offset being about 15 degrees (°) to 80° from the first and the second set of apertures.
 3. The current collector of claim 2, wherein a second offset being about 15 to 80° from the second and the third set of apertures.
 4. The current collector of claim 1 further comprising: a third set of apertures that extend from the first surface to the second surface of the material, the third set of apertures off-set from the second set of apertures.
 5. The current collector of claim 1, wherein the third set of apertures substantially aligned with the first set of apertures.
 6. The current collector of claim 1, wherein the first set of apertures being one of substantially triangular, circular, rectangular, elliptical, oval, and diamond.
 7. The current collector of claim 1, wherein the second set of apertures being one of substantially triangular, circular, rectangular, elliptical, oval, and diamond.
 8. The current collector of claim 1, wherein the third set of apertures being one of substantially triangular, circular, rectangular, elliptical, oval, and diamond.
 9. The current collector of claim 2, wherein the off-set minimizes variation in grid stiffness along transverse segments of the current collector.
 10. The current collector of claim 2, wherein the off-set increases grid stiffness uniformity along transverse segments of the current collector.
 11. The current collector of claim 1, wherein the first and the third set of apertures being substantially aligned.
 12. A current collector for a battery in an implantable medical device comprising: a material which includes a first surface and a second surface; a first set of apertures that extend from the first surface to the second surface of the material; a second set of apertures that extend from the first surface to the second surface of the material, the second set of apertures off-set from the first set of apertures in a range of about 15° to about 80°; and a third set of apertures that extend from the first surface to the second surface of the material, the third set of apertures off-set from the second set of apertures in a range of about 15° to about 80°.
 13. A method of forming a current collector for a battery in an implantable medical device comprising: providing a layer of conductive material; forming a first set of apertures in the conductive material; forming a second set of apertures in the conductive material, wherein the second set of apertures being off-set from the first set of apertures in a range of about 15° to 80°.
 14. The method of claim 13, further comprising: forming a third set of apertures in the conductive material, the third set of apertures off-set from the second set of apertures in a range of about 15° to about 80°.
 15. The method of claim 13, wherein the first set of apertures being one of substantially triangular, circular, rectangular, elliptical, oval, and diamond.
 16. The method of claim 13, wherein the second set of apertures being one of substantially triangular, circular, rectangular, elliptical, oval, and diamond.
 17. The method of claim 13, wherein the third set of apertures being one of substantially triangular, circular, rectangular, elliptical, oval, and diamond.
 18. The method of claim 13 further comprising: minimizing variation in grid stiffness along transverse segments of the current collector by off-set between the first and second set of apertures.
 19. The method of claim 13 further comprising: increasing grid stiffness uniformity along transverse segments of the current collector.
 20. The method of claim 13 further comprising: preventing at least one sharp bend in the current collector.
 21. An electrode assembly for an electrochemical cell, comprising a metallic current collector having major opposing surfaces, wherein said current collector possesses a characteristic variance in stiffness, wherein the variance in stiffness is the ratio of maximum stiffness to minimum stiffness, and said variance in stiffness has a value of between about one and about two.
 22. An assembly according to claim 21, wherein the metallic current collector comprises a substantially common thickness dimension and the characteristic variance in stiffness is due to the juxtaposition of a plurality of apertures distributed over at least a portion of said metallic current collector.
 23. An assembly according to claim 22, wherein at least some of said plurality of apertures are offset from adjacent apertures so that the stiffness of said metallic current collector being substantially uniform.
 24. An assembly according to claim 22, wherein a linear grouping of at least some of said apertures being offset from a horizontal reference plane at between about 15 degrees and 75 degrees.
 25. An assembly according to claim 21, further comprising at least one electrically conductive tab member coupled to a portion of the periphery of said metallic current collector.
 26. An assembly according to claim 21, wherein the metallic current collector comprises a first thickness dimension a second thickness dimension different from said first thickness dimension such that the characteristic variance in stiffness being due at least in part to different portions of the metallic current collector having either the first or second thickness dimension.
 27. An assembly according to claim 26, wherein the first thickness dimension is greater than the second thickness dimension and said first thickness dimension is disposed along a desired coiling region of the metallic current collector.
 29. An assembly according to claim 28, further comprising a plurality of apertures disposed over at least a portion of the metallic current collector.
 30. An assembly according to claim 29, wherein the current collector comprises at least one of the following materials: a copper material, a titanium material, an aluminum material, a tantalum material, a stainless steel material, a nickel material.
 31. An assembly according to claim 21, further comprising an alkali metal containing material coupled to the metallic current collector. 